[pgpool-committers: 4647] pgpool: First cut of primary server checking.

[Tatsuo Ishii]

First cut of primary server checking.

For now followings are implemented:

- Check all backend nodes starting node 0.

- If primary nodes appear twice or more, the second one or after are
  assumed invalid.

- Such invalid node will be degenerated at the next convenient
  time. Currently such timing is at the start up of Pgpool-II. This is
  apparently insufficient and should be improved later.

TODO:
- Verify primary nodes using pg_stat_wal_receiver.

- More chances to verify node status. Maybe in the same timing as
  streaming replication delay checking?

- Add new GUCs to control of this feature.

Branch
------
master

Details
-------
https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=f0631a6f260530616a5eb16b1538c2eb15abbac2

Modified Files
--------------
src/include/pool.h                            |  16 +-
src/main/pgpool_main.c                        | 201 +++++++++++++++-----------
src/streaming_replication/pool_worker_child.c |  61 ++++----
3 files changed, 166 insertions(+), 112 deletions(-)